Such a type of conventional cylinder device having a force multiplier is disclosed in Patent Literature 1 (Japanese Patent Application Publication, Tokukai, No. 2007-268625 A). The conventional technology is configured as follows:
A clamping rod, serving as an output rod, is inserted in a housing so as to be movable vertically. A first piston for rod is inserted in an upper part of the housing, and is fixed to the clamping rod. A first lock chamber and a first release chamber are formed above and below the first piston, respectively. A second piston for force multiplication is inserted in a lower part of the housing, and is fitted on the clamping rod so as to be movable vertically. A second lock chamber and a second release chamber are formed above and below the second piston, respectively.
By supply of compressed air in the first lock chamber and the second lock chamber, the second piston carries out force multiplication driving downward with respect to the clamping rod via a force multiplier.
Conventionally, the force multiplier includes: an engagement groove provided in a lower portion of the clamping rod; and a plurality of claw members swingably supported by the lower part of the housing. During the force multiplication driving, a tapered surface of the second piston, which has been driven downward, causes the claw members to swing inward in a radial direction, so that the claw members engage with the engagement groove.